GRB 060904

D. Grupe (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (GSFC/USRA), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU)
report on behalf of the Swift Team:

At 01:03:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060904 (trigger=227996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 237.743, +44.966 {15h 50m 58s, +44d 57' 57"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 3 little peaks
starting out and then a large peak at T+55 sec and a total burst duration
of about 85 sec.  The peak count rate was ~9000 counts/sec (15-350 keV),
at ~55 sec after the trigger. 

The XRT began observing the field at 01:04:27 UT, 66 seconds after the
BAT trigger. XRT found a bright, fading, uncatalogued X-ray source
located at RA(J2000) = 15h 50m 54.9s, Dec(J2000) = +44d 59' 07.8", with an
estimated uncertainty of 5.4 arcseconds (90% confidence radius). 
This location is 79 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 0.1s image was
2.7e-08 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 75 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical
3-sigma upper limit has been about 18.5 mag. The 8'x8' region for the
list of sources generated on-board covers 100% of the XRT error
circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to
E(B-V) of 0.02.

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David
W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL),
J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider
(PSU), and Daniel E. Vanden Berk (PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB060904 prior to the burst.  As these data should be useful
as a pre-burst comparison and for calibrating photometry, we are
supplying the images and photometry measurements for this GRB field
to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB060904

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=237.743 (15:50:58.3),
dec=44.9660 (44:57:57.6); Swift-BAT TRIGGER 227996), as well as 3
gri color-composite JPGs (with different stretches). The units in
the FITS images are nanomaggies per pixel.  A pixel is 0.396 arcsec
on a side. A nanomaggie is a flux-density unit equal to 10^-9 of
a magnitude 0 source or, to the extent that SDSS is an AB system,
3.631e-6 Jy.  The FITS images have WCS astrometric information.

In the file GRB060904_sdss.calstar.dat, we report photometry
and astrometry of 309 bright stars (r<20.5) within 15' of the
burst location.  The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected in
the u-band; use the errors and object flags to monitor data quality.

In the files GRB060904_sdss.objects_flux.dat and
GRB060904_sdss.objects_magnitudes.dat, we report photometry of
451 objects detected within 6' of the GRB position.  We have
removed saturated objects and objects with model magnitudes
fainter than 23.0 in the r-band.  The fluxes listed in
GRB060904_sdss.objects_flux.dat are in nanomaggies while the
magnitudes listed in GRB060904_sdss.objects_magnitudes.dat are
asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning that
they are very close to AB zeropoints and magnitudes are quoted
in asinh magnitudes.  Photometric zeropoints are known to about
2% rms.  None of the photometry is corrected for dust extinction.
The Schlegel, Finkbeiner, and Davis (1998) predictions for this
region are A_U=0.089 mag, A_g=0.065 mag, A_r = 0.047 mag, A_i=0.036
mag, and A_z=0.025 mag.

The file GRB060904_sdss.spectro.dat contains a list of the 3 objects
with SDSS spectroscopy within 6 arcminutes of the GRB position.
In addition to the redshift and 1-sigma error for each object,
this file also lists the object spectroscopic classification.

SDSS astrometry is generally better than 0.1 arcsecond per
coordinate.  Users requiring high precision astrometry should take
note that the SDSS astrometric system can differ from other systems
such as those used in other notices; we have not checked the offsets
in this region.

More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et al. 2006,
astro-ph/0601218).  See the SDSS DR4 documentation for more details:
http://www.sdss.org/dr5.

These data have been reduced using a slightly different pipeline
than that used for SDSS public data releases.  We cannot guarantee
that the values here will exactly match those in the data release
in which these data are included.  In particular, we expect the
photometric calibrations to differ by of order 0.01 mag.

This note may be cited, but please also cite the SDSS data release
paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using
the data or referring to the technical documentation.

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 060904 detected by SWIFT
(trigger 227996) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 26.8s after the GRB trigger
(9.4s after the notice). The field elevation decreased from
10 degrees above horizon and weather conditions
were excellents. First image was acquired during
the prompt phase.

Date of trigger : t0 = 2006-09-04T01:03:21.600

First image is 60.0 exposure trailed. No OT is visible
in the XRT error box (Grupe et al. GCNC 5502)
t0+26.8s to t0+86.8s : R > 16.0

Second image is 30.0 exposure. No OT is visible:
t0+93.7s to t0+123.7s : R > 17.3

We co-added a series of exposures. No OT is visible:
t0+93.7s to t0+376.2s : R > 19.5

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon= 71.6566 lat=+50.2105
and the galactic extinction in R band is 0.0 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.